While rainfall rates increase whether the long-term warming trend is natural or not, the rate of increase appears to be higher during natural warming trends.
The result might help resolve a long-standing discrepancy between changes in rainfall projected in global climate models and changes projected by studying the historical record, researchers say...............
Are human-caused and natural global warming different? Study says yes.
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Global warming has not stalled, insists world's best-known climate scientist....
ΑπάντησηΔιαγραφήProf James Hansen warns public not to be fooled by 'diversionary tactic' from deniers
Suggestions that global warming has stalled are a "diversionary tactic" from "deniers" who want the public to be confused over climate change, according to the world's best-known climate scientist. Prof James Hansen, who first alerted the world to climate change in 1988, said on Friday: "It is not true that the temperature has not changed in the two decades."
Since 1998, when the Niño climate phenomenon caused global temperatures to soar, the rate of increase in warming has slowed, causing some sceptics to suggest climate change has stopped or that the effect of rising carbon dioxide levels on climate is not as great as previously thought.
Prof Hansen, speaking to BBC Radio 4's Today programme, rejected both arguments. "In the last decade it has warmed only a tenth of a degree compared to two-tenths of a degree in the preceeding decade, but that's just natural variability. There is no reason to be surprised by that at all," he said. "If you look over a 30-40 year period the expected warming is two-tenths of a degree per decade, but that doesn't mean each decade is going to warm two-tenths of a degree: there is too much natural variability."
Prof Hansen said the focus by some on "details" was a smokescreen. "This is a diversionary tactic. Our understanding of global warming and human-made climate change has not been affected at all," he said. "It's because the deniers [of the science] want the public to be confused. They raise these minor issues and then we forget about what the main story is. The main story is carbon dioxide is going up and it is going to produce a climate which is going to have dramatic changes if we don't begin to reduce our emissions." In 2008, scientists anticipated an upcoming slowing in temperature rises.
Prof Hansen, who recently stepped down from his Nasa post after almost 50 years to focus on communication, said the forecast impact of climate change was little affected by the recent slowdown in the rate of rising temperatures.
"Climate is a complicated system but there is no change at all in our understanding of climate sensitivity [to carbon dioxide] and where the climate is headed," he said. "Our understanding of sensitivity is based on the Earth's history, not on climate models, and we have good data on how the Earth responded in the past when carbon dioxide changed. So there is no reason to change the forecast for the long term." On 9 May, a new study of lake sediments from a remote meteorite crater in Siberia showed temperatures in the region were 8C higher the last time CO2 levels were as high as they are today. Last week, atmospheric CO2 concentrations reached the milestone 400 parts per million, for the first time in millions of years.
Prof Hansen has caused controversy in the past with statements including "CEOs of fossil fuel companies should be tried for high crimes against humanity and nature" and the assertion that "coal-fired power plants are factories of death".
http://www.guardian.co.uk/environment/2013/may/17/global-warming-not-stalled-climate
17/5/13
Human role in warming 'more certain' - UN climate chief...
ΑπάντησηΔιαγραφήScientists are more certain than ever that greenhouse gases from human activities are heating the planet, the head of the UN's climate panel says.
Rajendra Pachauri made the comments in an interview with BBC News.
The panel is due to deliver its latest report on the state of the climate later this week in Stockholm, Sweden.
Its last report was criticised after an error on glaciers unveiled other flaws, but Prof Pachauri said procedures had been reformed and strengthened.
He also dismissed suggestions of a slowdown in global warming.
"There’s definitely an increase in our belief that climate change is taking place and that human beings are responsible,” he told me.
"I don't think there is a slowdown (in the rate of temperature increase). I would like to draw your attention to the World Meteorological Organization which clearly stated on the basis of observations that the first decade of this century has been the warmest in recorded history.
"And I think the rest will be brought out by the report itself when it’s released."
Prof Pachauri’s insistence that warming has not slowed hints at a focus of debate this week in Stockholm: Global temperatures have not been increasing as fast as scientists predicted, and several governments insist that this puzzle is properly addressed in the final summary.
Have computer climate models overestimated the sensitivity of the planet to increasing CO2? Or has excess heat been stored up in oceans whence it will emerge to super-heat the planet in decades to come? Or both?
Or just perhaps it could be something else.
Unprecedented change
The draft says a doubling of CO2 concentrations in the atmosphere above pre-industrial levels (expected by mid-century) is likely to result in a temperature rise globally of between 1.5 and 4.5C.
Any rise above 2C could risk major changes on Earth, according to projections, but the results of recent modelling involves a downward tweak at the bottom of the range, offering the tantalising prospect to politicians that if humans are very lucky, they could get away with rising CO2 emissions for a bit longer than previously expected.....http://www.bbc.co.uk/news/science-environment-24204323
23/9/13